ARC LAMP

device for producing light by maintaining an electric arc across a gap between two conductors; light comes from the heated ends of the conductors (usually carbon rods) as well as from the arc itself. Arc lamps are used in applications requiring great brightness, as in searchlights, large film projectors, and floodlights. The term arc lamp is usually restricted to lamps with an air gap between consumable carbon electrodes, but fluorescent and other electric discharge lamps generate light from arcs in gas-filled tubes. Some ultraviolet lamps are of the arc type. Sir Humphry Davy constructed the first arc lamp (1807), using a battery of 2,000 cells to create a 100-millimetre (4-inch) arc between two charcoal sticks. When suitable electric generators became available in the late 1870s, the practical use of arc lamps began. The Yablochkov candle, an arc lamp invented by the Russian engineer Paul Yablochkov, was used for street lighting in Paris and other European cities from 1878.